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Alfa Romeo Supercharging
Supercharging book: 117 pages, full color
Now available on Amazon.com search by the title and author below
Supercharging. A guide to superchargers, water injection, and a lot more
by Greg Gordon
It has taken over two years to write, but now it's done! If you intend to build your own supercharger kit, or if you are looking to get the most out of an existing kit, this book is for you. It covers a lot of subjects, :supercharging history, types of superchargers and advantages of each, water injection in great detail, fuel injection, bypass and blow off valves and intercooling. It has about all the information you need to design and build your own supercharger kit. It also has charts to show pulley ratios needed for various levels of boost for 45, 62, and 90 cubic inch superchargers on various engine sizes from 1.0 to 5.0 liters. It has charts for water injection, a list of superchargers that can be found on cars at salvage yards, evil bay, etc. It has power and temperature charts for various blowers. It describes in GREAT detail the advantages of turning a smaller supercharger fast for a given level of boost as well as the advantages of a big supercharger turning slowly. This will really help you choose the right supercharger for your goals. The book is in full color, and it has lots of helpful pictures and charts.
Call Misty (918) 760-0668 to order. Or send to paypal firstname.lastname@example.org
SUBJECT: Supercharging Book
Supercharger kits Alfa V6 - these are still being made by Toby Smith (contact greg for info)
Alfa 4cyl, TBA
We make a supercharger kit for the Alfa Romeo GTV6 and Milano in house at our shop. The kit uses the Eaton/Magnuson MP62. The kit has now been proven on both the U.S. spec 2.5 and 3.0 with dyno results and 30,000 miles of travel on one car to back it up.
The standard MP62 supercharger can be set up to provide anywhere from 5 to 14 pounds of boost on the 2.5 liter engine and 5 to11 pounds on the 3.0 liter. That's assuming the motor will be kept within a few hundred rpm of the factory redline ( I based this on a 6500 RPM redline for the 2.5 and a 6000 RPM redline for the 3.0).
Basic kit is . This includes the supercharger, nose drive assembly, pulleys for the crankshaft, supercharger and tensioner, intake and discharge ports, mounts, brackets, belt, bypass valve and a few other things.
The kit can be set up with either stock Bosch L-Jetronic fuel injection or an aftermarket unit. Water injection is highly recommend and an intercooler can be fit if desired. We don't have a one size fits all specification list. The number of options for water injection alone are massive with prices ranging from a simple $300 kit up to almost $1000. We use and strongly suggest the Cooling Mist brand of water injection.
We have a 200 hp kit. thing needed to supercharge your 2.5 and bring it up to 200hp. It's a low boost kit that retains the stock fuel injectors and L-Jetronic system. It's a non intercooled kit that includes the supercharger discharge piping, intake plumbing, bypass valves, silicone hoses, couplers, clamps, and all needed hardware to adapt the stock fuel injection system to the supercharger. It's is truly a complete kit, and it's easy to install.
Pictured below is the basic kit plus a discharge pipe, silicone couplers and clamps. This is a typical non intercooled configuration. I think it's a very elegant looking supercharger kit that really adds the the beauty of the Alfa Romeo V6.
This kit can provide a big increase in power by itself. Using pump gas an otherwise completely stock 2.5 can put out about 220 horsepower. My 2.5 put out about 250 hp with a MP62x at 10 psi and with programmable water injection. That's a stock engine using L-Jet! A stock 3.0 with this kit and bigger injectors can put out about 270 horsepower! Obviously with headers, an intercooler, etc a lot more power can be had. We recently built a customer car that puts out about 325 horsepower with an intercooler, SDS fuel injection and just 7.5 pounds of boot. That's on a stock motor including the factory manifolds and an intact converter!
When comparing levels of power it's very important to look at the entire horsepower and torque curve, not just the peak horsepower number at high rpm. As one top Alfa guru likes to say, "horsepower sells cars, torque wins races". Most supercharged Alfa V6s have massive torque throughout the entire rpm range. We normally see around 200 lb./ft of torque at the wheels with the 2.5 throughout most the the rpm range, and about 250 with the 3.0.
Pictured below is a supercharged 2.5 in a GTV6. This car puts out 230 rear wheel horsepower and 205 rear wheel torque. It has about 200lb of torque at the wheels from about 2000 rpm up to the 7000rpm redline. It's set up with forged non interference pistons and runs 10psi of boost through an intercooler.
The engine pictured above has 8.5:1 compression and water/methanol injection. It can actually run just fine on 87octane (r+m)/2 fuel. Without the water injection it runs fine on 91octane (r+m/2) fuel.
An intercooler is not needed, however adding one will provide an increase in air density and allow higher boost resulting in more power. Liquid to air types are very effective. There are two types that fit pretty well. The PWR brand fits well and is highly thought of in the forced induction world. The GMC Syclone intercooler also fits well, provided you don't have a distributor. So if you are upgrading to a crank fired ignition system the Syclone unit is a good chioce. For air to air types that fit contact me.
The GMC Syclone unit is super effective. At a recent track day, I rode in a customer car on a day with an outside air temp of about 77F. Lap after lap the intercooler held temps down, we never saw more than 95F in the intake plenum.
Our kit is designed with servicing the car in mind. NOTHING related to the supercharger kit needs to be removed for normal service. You can change spark plugs, wires, oil and filter without removing any supercharging system components. It's actually even easier than on a stock engine. Even the head covers (valve covers) can be removed without taking anything else apart. This stands in stark contrast to many other forced induction kits. There is a turbo kit out there for Corvettes that restricts access so much it takes 6 hours to change the spark plugs. We put a lot of thought into this issue.
The picture below shows a supercharged 2.5 in for service.
This engine pictured above is probably the most crowded GTV6 engine bay possible. It has a supercharger, Syclone intercooler, and water methanol injection. It has airconditioing that works well, a windshield washer system and everything else you would find in a stock GTV6. It also has cruise control, and a complex alarm system. Yet, with all this stuff servicing is eaiser than on a stock engine. The head covers come off with everything in place.
The engine pictured below was built by a customer using our kit. He went with the PWR intercooler
This customer went with my basic supercharging kit and forged non interference pistons but did his own thing for about everything else. It uses a PWR intercooler with custom pipes. The car looks great, and I hear it runs very well.
This next car features the very first supercharger kit I sold!
The racecar pictured above runs a very early version of my supercharger kit. It is a regional SCCA autocross champion. In fact, it is the only V6 Alfa I know of that's an SCCA regional champion. This is currently the most powerful car I know of that uses my supercharger kit. It has 291 rear wheel horsepower and 313 rear wheel torque (about 355hp and 380tq at the flywheel). The owner tells me that even with the HUGE wheels and tires it can break the rear tires loose with supercharged power. It has modern engine management and a PWR intercooler.
Our 4cyl Alfa Spider kit is in testing. The bulk of the testing was done with a 4cyl engine in a Milano. It has well over 15,000 trouble free miles on it. This new kit is great, it's an improvment in nearly every way over my V6 kit. It's eaiser to mount, it's lighter, it's almost silent during normal driving, it has more power potential per cc of engine displacement, etc. As soon as I have it installed in my Spider it will be for sale. Expect a 40% increase in power on a stock engine, with far greater gains on modified engines. We plan to offer a package with modern fuel control, discharge piping, silicone couplers, and water injection. As always, you can buy just the basic kit and do your own thing.
Of course all our dyno testing is done on a chassis dyno that measures rear wheel horsepower. We calculate flywheel horsepower figuring an 18% driveline loss. There is a lot of debate over just what the driveline losses are but a stock 154 horsepower 2.5 has about 125 horsepower at the wheels, and a stock 183 horsepower 3.0 has about 145 at the wheels, at least on the dyno we use, so the 18% rule seems about right.
Supercharger crankshaft pulleys Alfa Romeo GTV6 and Spider $195
These pulleys bolt to the factory crankshaft on the Alfa Romeo GTV6 and one bolts to the 1982-1989 Alfa Spiders. The pulley in the upper left corner is our older style GTV6 pulley and it's made of steel. This older style steel pulley is being phased out. All the newer pulleys are aluminum and hard anodized for long life. Going around clockwise, the next pulley is the new style GTV6 pulley. The next one is an oversize GTV6 pulley for extreme applications. In most cases this pulley will require notching the front crossmember. If you are using a GTV6 crank pulley on a Milano it will fit without notching the crossmember, but just barely. It would be better to notch it. The pulley in the bottom left corner fits the 1982-1989 Alfa Romeo Spider.
I have held off using aluminum crank pulleys for a long time but the rotating mass savings has become too hard to ignore.
For supercharging purposes the GTV6's crank pulley is superior. If overhauling a Milano engine for serious supercharging work, converting it to a GTV6 crank pulley will allow use of a larger supercharger crankshaft pulley.
Spider Crankshaft stock replacement pulley with electroless nickel plating and extra timing marks.
We do not always keep these in stock. Call 918-760-0668
The 1982-1989 Alfa Spiders equipped with air conditioning have a serious problem with the factory crank pulleys cracking near the key way. The problem is so severe that there is a waiting list to get used replacements at the nations primary Alfa Salvage yard. We have designed a replacement pulley that will never crack or fail. It has both factory belt slots as well as provisions to attach a 6 rib supercharger pulley. It's the ultimate solution for this problem. The prototype pulley is pictured here, the production version will be the same except for some minor lightening work.
This pulley is a direct fit replacement for the stock pulley and includes the factory timing marks.
This pulley will fit all Alfa L-Jetronic and Spica 2 liter engines. Although it fits the Spica engines, it does not have provisions to drive the Spica pump so it's only usable on Spica cars converted to some other fuel delivery system (Webers, SDS, Gotech, etc.). Air conditioning equipped L-Jet cars will need to retain their forward flange plate that bolts to the front of the factory crank pulley.
Electroless nickel plating provides a tough long lasting finish that looks great. It will prevent rust and is far superior to paint. The extra timing marks allow performance oriented uses to dial in very accurate timing settings.
Call Misty 918-760-0668 to order. Or send to paypal email@example.com
SUBJECT: AR Spider Crankshaft Pulley
Note: All will be shipped insured using USPS. You may have to sign for them.
Forced induction non-interference pistons: Contact us for pricing. Allow 60 days for these to ship, hopefully it would be sooner but I am not stocking these babies so I am at Venolia's mercy.
3 liter: I think these are the ultimate Alfa 3.0 12 valve pistons. They are true forged pistons with 8.8:1 compression. This decrease in compression allows for rear wheel horsepower levels above 300 on pump gas with a well set up intercooled forced induction system. Yet it's high enough that the engine will behave normally during normally aspirated operations. Of course with water injection and or race fuel, truly insane power numbers can be reached. All these pistons now come with pin oilers standard for extreme duty use.
Perhaps best of all, with stock cams they are non-interference which means that with a timing belt or belt tensioner failure the valves won't hit the pistons! If you are using higher lift cams, or have milled your heads they won't be truly non-interference but the chances of disaster will be greatly reduced.
Because these are true forged pistons they are ultra strong. Piston strength will not be an issue. Set up correctly per our instructions they don't rattle in the bores and don't smoke during cold running. They will cause higher oil consumption during the warm up period due to their high expansion rate as compared with conventional stock cast pistons. That's really their only drawback. Keep in mind virtually all aftermarket products or modifications have drawbacks. This one is pretty minimal!
They are slightly overbore, just .010 so you can re-use your old liners by boring them. No need to buy new liners. Instructions for boring liners can be found on the SuperVerde page. It's quite inexpensive. If you don't want to do that, send us your liners and we can have them bored for an additional cost.
2.5 liter: The 2.5 pistons are essentially the same design with two changes. They are 8.5:1 compression to allow for more boost and they have even more clearance for the valves. They are non interference with stock cams, 164S cams or most of the streetable cams available.
We carry THS connecting rods. These rods are very high quality and can handle 700 horsepower and more rpm than you will ever need. They are the nicest connecting rods I have ever seen. If you are building an engine for extreme levels of power and or high rpm use, these rods are a good investment. Please allow 2-4 weeks for delivery. We do not always keep these in stock.
Here is the connecting rod kit.
These rods are beautiful.
Here is what THS says about them:
"Forged Steel Conrods
I wish to add a few things.
Connecting rods take an incredible amount of abuse in an engine. Horsepower puts compressive stress on them, and rpm creates expansion stress. In the case of the Alfa V6, the STOCK rods are very strong in terms of compressive stress and sort of marginal at handling expansive stress. In other words, they probably won't fail due to moderate power increases, but an increased rpm limit will quickly kill them. A combination of more power and more rpm creates even more stress.
I know from previous experience that people will ask if they "need" these rods. Of course "need" is highly subjective and depends a lot on the driving style of the individual user, plus about a million other variables. Here are my thoughts on rods:
1. I am very comfortable with stock rods and 300+ horsepower provide the redline is kept to about 6000rpm for the 3.0 and 6500rpm on the 2.5. Stock rods that are prepared for performance are even better.
2. On a mild normally aspirated engine, the stock rods are just fine up to about 6500 on a 3.0 and about 7000 on a 2.5.
3. If you plan on exceeding 350 horsepower I suggest using upgraded rods regardless of the engine's redline.
4. If you plan on exceeding 6500rpm on a 3.0 or 7000rpm on a 2.5, especially for extended periods of time, I would use upgraded rods regardless of horsepower.
5. If your engine will exceed both 350 horsepower AND 6000rpm/6500rpm for the 3.0 and 2.5 respectively I consider upgraded rods to be a must use item.
Obviously these numbers are somewhat subjective. I am not going to go out and test a dozen engines to destruction to verify all of this. However these numbers are better than simple guesses. I do know of a few Alfa V6s that suffered connecting rod failures, and I have built some powerful motors that held together, so I have some decent guidelines to follow.
Rods + Priority US is $923.95
Rods + Priority Canda is $942.95
Rods + Priority International is $963.95
Call Misty (918) 224-4646 or (918) 760-0668 to order. Or send to paypal firstname.lastname@example.org
SUBJECT: AR Connecting Rod Kit
Note: All will be shipped insured using USPS. You may have to sign for them.
Forced induction myths. This will upset some people.
I am writing this section to counter some of the misinformation in various internet forums and a few automotive magazines. It's semi advanced and if you don't know the difference between a Centrifugal and a Roots supercharger please read my descriptions on Supercharging in the Technical Articles section on this site. Each of these systems have advantages and disadvantages and all can give outstanding results.
Some of the most knowledgeable people on the planet post information on the net. However far more uniformed people post information. It's tough to sort out the good information from the bad. Sadly there is about twice as much misinformation as there is good information. Magazines are a little better. At least the writers of those articles have some basic qualifications. One problem with them is that magazines are beholden to their advertisers. Most can't stay afloat from subscription revenue alone. This tends to create articles which are written from a certain point of view not likely to be overly critical of any product. Books are a great source of information. In some cases authors make errors but it's usually a case of an honest mistake. I own nearly every supercharging book in publication and all but one are very good.
The best, most accurate and unbiased information we can get on forced induction is from our own government. Prior to the Jet age the government agency N.A.C.A. or the National Advisory Council on Aeronautics did an incredible amount of research on piston engines and a large amount of it was devoted to forced induction. During World War II they had all the best piston engine experts in the country working for them with a nearly unlimited war time budget. They could build whatever test equipment they needed and test anything to destruction. Some might claim that since the reports they generated are old they are no longer valid. Nothing could be further from the truth. Engine basics have not changed, what worked then works now. The equipment they were testing was built with a wartime budget and while it might not be as good as modern military spec. hardware it was at least as good as the stuff we now have in the automotive aftermarket. For example in 1938 military aircraft engines had superchargers with an adiabatic efficiencies of 75%. They were up over 80% in laboratory testing just a few years later during the war. Those numbers are about the same as the very best automotive units today. The only real drawback is that the reports are written with a lot of aviation and not automotive terms. For example they never talk about supercharger or turbocharger boost, they talk about critical altitude. Now as an active pilot and flight engineer I can convert all of this information into automotive data. A critical altitude of 20,000 feet requires about 8 pounds of boost. Nearly everything I write on forced induction is backed up by data in the N.A.C.A. reports.
So without further delays lets blow holes in some of the B.S. out there.
Myth 1: The energy it takes to spin a turbocharger is free.
I love turbochargers as much as anybody. In fact my daily driver is a turbo car, but if I had a nickel for every person that incorrectly claims the energy to drive a turbocharger is "free" I would be a rich man. The turbocharger's drive system is more mechanically efficient than the belt on a supercharger but it's not free. The most basic laws of physics say that nothing is free. Some people have changed the terminology to say that the turbo is driven by "wasted energy". That's more nonsense. The energy needed to expel the exhaust from the combustion chamber is not wasted, in fact it's rather essential. Many makers of Turbo kits phrase it another clever way. They say that the energy needed to drive the turbo is "not taken directly from the crankshaft like it is with a belt driven supercharger". Ok, well at least that's basically true although somewhat misleading. It may not be taken "directly from the crankshaft" but it is taken from the engine. So how is the energy taken, and how much is used?
Here are the facts as reported in many N.A.C.A. reports. Exhaust drives the turbocharger and that causes exhaust backpressure robbing power as surely as if the compressor section was connected to a belt. It may not rob as much (it's possible under some conditions it will rob more) but it does rob power. Here is a quote from N.A.C.A. " When an exhaust turbosupercharger is used, the net engine power is the total engine power supercharged less the reduction in power due to increased exhaust back pressure." So there you have it, turbos cause exhaust back pressure taking power away from the motor. The report goes on to say just how much the loss from exhaust back pressure is going to cost and I assure you it's not free. If it was, then all the efforts made in the performance industry to reduce backpressure via special mufflers, headers etc. would be wasted. So just how much power will the turbo consume? They compiled a ton of data on that. It will vary somewhat from motor to motor, even between two theoretically identical motors. The number they came up with is 6.2% of total engine horsepower when using 10 pounds of boost. That's assuming exhaust pressure in the manifold between the combustion chamber and the turbine is equal to intake manifold pressure. It's important to understand, that's a best case scenario. A turbo car will need very good unrestrictive equal length exhaust manifolds and a perfectly sized turbocharger to achieve this. I suspect the best manifolds made for race cars by masters like Jim Steck or the mad South Africans are good enough to get these results. In practice when limited by engine compartment space, strength requirements and other factors it's not likely you will find a manifold this good on a street Alfa. Many turbo cars have double the intake pressure in the exhaust manifold prior to the turbine. At 10 pounds of boost that would cost about 15.3% of the engine's horsepower using N.A.C.A.'s formula.
Time to plug in some real world numbers. A MP62 supercharger providing 10 pounds of boost on an Alfa 2.5 will use about 27 horsepower. It could potentially use less with optimal piping, but on my car it uses 27 horsepower so that's real world data. My car has about 250 flywheel horsepower so using N.A.C.A.'s formula a very efficient turbo set up would need 15.5 horsepower to drive the turbo. While there is no doubt that 15.5 is less than 27, it's a factor that's small enough to be offset in other areas. Now using the same formula a turbo with a restrictive type of exhaust manifold will use 38.25 horsepower.
My point here is not to say that belt driven superchargers are better or worse. The point is that according to the best engineers in the U.S. at the time working with a nearly unlimited wartime budget determined that the energy to spin a turbocharger is not free. I am sure the brainwashed free energy crowd will state that these reports are old and turbos have come a long way. Of course if free energy was used to spin a turbo then it wouldn't matter how much they improved in this regard. An improvement of any percentage times zero is still zero. In other words if they are free now because they are twice as efficient as the older units the math says the older units must have been free too.
Myth 2. Battle of the Boost.
One major automotive magazine published an article titled "Battle of the Boost" a few years ago. It probably should have been called, battle to keep subscribers and advertisers happy. This article is constantly quoted in internet forums. It's usually quoted by people who just flipped to the results page of the article without reading the whole thing. The article was intended to be a comparison of a turbocharger, a centrifugal supercharger and a Roots supercharger on a small block Chevrolet V8. All 3 were non intercooled and set up for 9.5 pounds of boost.
The results showed that the Roots won out at low speed, the turbo in mid range and the centrifugal at very high RPM. The centrifugal passed the Roots in power at about 4000 rpm on the way to the engine's 6000 rpm redline. In summary all three types looked pretty good and a solid argument could be made for any of them. This keeps the advertisers and the loyalist of each type of device happy. However the conditions of the test were strongly adjusted against the Roots blower.
Here is what they did. The Roots blower they used was a model currently in production, however it's an ancient design. The Roots blower they used had two STRAIGHT lobes per rotor. This design literally dates back to the Civil War. Modern Roots blowers like the Eaton have three lobes per rotor and they have a 60 degree helix built into them. The older design takes far more power to drive and heats the air up an incredible amount compared to the newer type. The reasons are somewhat complex but the short version is this. Twin lobe straight rotors discharge the air in an on and off pusling action. This heats up the air because it's constantly moving back and fourth. Triple helical lobe set ups discharge air constantly greatly minimizing these pulses.
The next factor working against the Roots was fairly obvious. It was not able to put out 9.5 psi due to pulley limitations. Now I don't know why that is. Did they just not have the right pulley? Did the proper pulley not fit the snout? Was the carburetor too restrictive? I don't know. What I do know is that an ancient design Roots at 8 psi is not going to compete favorably with the most modern centrifugal made running at 9.5 psi. It's just not a valid comparison. Had they used a Magnuson MP112 at 9.5 psi it would have been another story.
Myth 3: Replacing the Eaton M112 with a Lysholm design supercharger on a 2003 or 2004 Mustang Cobra will gain over 100 rear wheel horsepower at 13 pounds of boost .
This particular issue is the most disturbing to me. Most of these myths are the result of concepts that are difficult to understand. This myth appears to have been intentionally created. I feel that the manufacturer involved here intentionally designed a misleading test which resulted in this myth. The editor of a major performance magazine stood by the test either because he didn't understand the test conditions or he just wanted to appease his advertiser. The sad thing here is that the manufacturer involved makes a GREAT supercharger. If you want to run 20psi on your 2003 Cobra a screw supercharger is the way to go. That's way outside the operational range of the car's original Eaton because it's simply not big enough for that job.
One manufacturer of a screw supercharger kit has a report out there that was done under conditions that were heavily biased towards the screw supercharger. The results of this test are constantly thrown around by people who didn't read or understand the whole test. I can understand a manufacturer biasing the test in their favor. They didn't cheat, they just came up with an ideal scenario for their product.
Here is the deal. Some guy on the net posted results of his modified Eaton car vs a similar car with an aftermarket screw type. The screw supercharger put out more peak power but the car with the Eaton appeared to have a little better overall power curve. Now it's certainly possible the screw supercharged car did not have optimal tuning but it was still an interesting comparison as it showed that under certain conditions both types could be in the same ballpark.
The maker of the screw supercharger kit fired back saying that the car in the test must have had a bad tune and then posted their own test with both cars putting out 13+ pounds of boost at a mid range RPM level showing a screw supercharged car putting out over 100 more horsepower at the wheels. I consider this test to be highly misleading. When I first heard about it from some self proclaimed experts the version I heard was that the screw put out over 100 more horsepower at the wheels at the same level of boost. I knew right away this was nonsense as even if the screw supercharger used zero power to drive and didn't heat up the air at all it wouldn't have that much more power over the Roots at 13+ psi.
A thorough review of the test revealed the following facts. The increase of over 100 horsepower was not at the same boost level. The screw was over 16 psi and the Roots at 9.5. That's a huge difference. The trick here is that they used a screw supercharger sized in such a way that boost increased a lot with RPM so while both were at about the same boost level at mid range RPM the screw had much higher boost at redline. This is pretty easy to do. You take a supercharger that's oversized for its application and it will turn slowly and operate in a range where it has a steep volumetric efficiency curve. This results in boost increasing greatly with RPM. Had the Roots been set up to provide 16 psi at redline it would have had far more boost in mid range and would have outpowered the screw at lower and mid range RPM due to the flatter boost curve of a fast spinning Eaton.
The chart below shows why a larger supercharger's boost tends to increase with RPM.
As you can see in the chart, if a typical positive displacement supercharger is sized so that it operated in the lower RPM range on a given application, boost will increase greatly as the engine speeds up. Of course that defeats the whole idea of using a positive displacement blower in the first place. If you want boost to increase with RPM use a centrifugal supercharger. On the same engine, a properly sized positive displacement blower will operate in the higher range where the boost will stay relatively constant throughout the RPM range.
Like they say on T.V. "but wait there's more". Why did the Eaton have only 9.5 pounds of boost at redline when it had 13.5 at mid range rpm? They don't explain that in the report. I can say with certainty that boost does not fall off with an Eaton unless something is wrong. Keep in mind my Alfa with a MP62 has almost the exact same supercharger size to engine size ratio as the Eaton car in this test. In most cases boost falling off with the Eaton means the belt is slipping. As I wasn't there and I don't work on the same engines I can only speculate why the belt might have been slipping. The Eaton did use a much smaller pulley as it's a smaller supercharger. This decrease in pulley area may have combined with travel limitations of the belt tensioner to allow the belt to slip. The screw supercharger has a bigger pulley so the belt has more to bite and the supercharger kit certainly takes belt tension into account.
To top all this off both superchargers were run with the same tuning specs. I have no doubt that the tuning specs used were the specs designed for the screw supercharger, not the Eaton.
So we have an increase of well over 100 horsepower with the screw supercharger. However it's based on a 69% increase in boost. That's about as far from an apples to apples comparison as you can get.
Now for my non B.S. version of this test. Yes, screw superchargers are more efficient from a pure power standpoint. This is especially true during dyno testing or at the race track because the Roots cooler off boost temps don't have a chance to let the intercooler chill.
In this test the Screw supercharger put out slightly more power at the same level of boost which occurred at about 3500 rpm. At this point with equal boost the Roots put out about 325 at the wheels vs about 335 for the screw. That's hardly a massive increase. Especially when you consider the source of the test and the amount of money involved in this upgrade. At max power RPM the Screw supercharged car put out 25% more horsepower but it took 69% more boost to do it. When you factor in the Roots advantages in an apples to apples comparisons it becomes clear why it's the device of choice among Aston Martin, Lotus, G.M. Ford, etc. Those big manufacturers didn't go with an Eaton supercharger because I told them to. They didn't even ask me. They went with the Eaton because they did their own testing and research and determined it's the best unit for the job.
It's possible to take ANY supercharger and design a comparison test where it will come out looking better than ANY other supercharger. It's really not hard to do. Be very wary of supercharger comparison tests, especially done by organizations with a financial stake in the results like manufacturers and magazines with advertising. Your best defense is to learn and understand how these things work. Then read the tests carefully. They very rarely lie in these test, they just design the test to favor a certain product.
Myth 4: Overlap is bad!
Ok, the myth here is that on a supercharged motor any cam with any amount of overlap is bad. The theory being that boost will escape out the exhaust along with all the fuel while both intake and exhaust valves are open. Now valve overlap can be bad. If an engine has exhaust pressure higher than intake pressure like most turbocharged motors then it's possible for exhaust to dilute the intake charge during an overlap period. It's also possible to use so much overlap that a belt driven supercharger won't be able to provide much boost because it can escape out the exhaust valve. This is especially bad with an internal compression type supercharger (i.e. a Lysholm screw type, or a centrifugal) as the motor will have to use power to generate boost it won't use. However the right amount of overlap will help a supercharged motor. Here is a quote from General Electric. "Maintaining a high manifold pressure ahead of the intake valves allows the use of "valve overlap" in the engine, so that the intake valve opens just before the exhaust valve closes at the end of the exhaust stroke. This allows the compressed mixture from the intake manifold to scavenge the spent gases out of the clearance volume of the cylinder and also to improve cooling of the exhaust valve." In case you are wondering why G.E. cares about valve timing, it's because they built most turbochargers and superchargers for the military during World War 2.
Overlap can be bad. However on a supercharged motor the right amount will be good.
Myth 5: Only turbochargers can have adjustable boost without changing pulleys.
Turbochargers have the most efficient means of control. It's also possible to control boost from the driver's seat in a supercharged car. My GTV6 has in car adjustable boost set up pretty much the way N.A.C.A. did it. It's not as efficient as the adjustment method used for a turbo but it's pretty good. It's possible to have adjustable boost in a car with a Lysholm or centrifugal however it's not efficient.
Here is what N.A.C.A. says on the subject. Regarding a turbocharger's waste gate system they said it's "an excellent method of control". Regarding the Roots they said it's "not so satisfactory as that used by the exhaust turbosupercharger". The centrifugal did not come out so well in this area. They said it was "very unsatisfactory from the standpoint of net engine power when compared to the method used on the Roots or turbocentrifugal superchargers". By turbocentrifugal superchargers they mean turbochargers. As far as I know there hasn't been any good study regarding varying the boost on a Lysholm but as it's an internal compression device I think the results would be identical to the centrifugal.
Myth 6: Water Injection is Chemical intercooling.
Ok, now I love water injection. I use it on my car and I would not build a forced induction car without it. However it's not an intercooler. An intercooler increases air density by cooling the air. Water injection provides very little increase in density. It does cool the air a lot but it does it in such a way that the density increase is minimal if it exists at all.
Consider a cylinder, better yet a scuba tank. The scuba tank has air in it. If we cool the tank pressure inside will change however the density of the air inside will not change. Why not? Simple, we have not added any air molecules to the volume of the tank. This scuba tank is much like the cylinder in your engine once the valves are closed. The great majority of the cooling with water injection takes place during the compression stroke when the valves are closed. Very little takes place prior to the cylinder.
Of course N.A.C.A. did a lot of tests with water injection. They found that the density of the air only slightly increased with water injection. Here is what they said, "The fact that the amount of air mass inducted increased so slightly with the quantity of water injected seems to indicate that vaporization was taking place within the cylinder rather than within the inlet pipe." Keep in mind they got this small increase in a laboratory with an engine running at a constant speed. It's doubtful you could get even the same small increase when you consider all the variables on a real car. If you have a very good and expensive system like Cooling Mist's controller system (and certainly with their "Cooling Commander" system) you should be able to get it but the density increase will still be small compared to an intercooler.
An intercooler provides an increase in air density by cooling the air prior to the cylinder. Water injection provides only a small increase in air density and then only under ideal conditions. Under most real world conditions the decrease in density caused by the increase in humidity offsets what little cooling takes place outside the cylinder. The benefit of water injection is the massive amount of detonation protection it provides by cooling the charge air within the cylinder. In other words it allows you to run more boost and or more advanced ignition timing.
Think of it this way, an intercooler provides a significant increase in air density and relatively little detonation protection. Water injection provides very little increase in air density but gives massive detonation protection. Ideally you should have both. If I had to choose just one I would lean toward water injection.
One more thing on this subject. An air temp gauge may show a big drop in inlet temperatures when the water injection turns on. However that's largely due to the wet thermometer syndrome, not due to a big drop in actual temperature.
That's it for the anti myth section of my website. Of course there are a lot more, the myths surrounding water injection alone could take me days to type.
Thanks for reading and happy driving.
There have been a few people who stated that modern large turbos can have much lower backpressure numbers than those N.A.C.A. reported. That may be true, then again, for all the big talk, nobody has come forward with one shred of verifiable evidence of this. Most of these claims relate to very large turbos on race cars and report numbers of around 20psi of boost at the intake valve and 10psi above ambient between the exhaust valve and the turbine. The important factor here, is that even if these numbers were accurate and verifiable, they still make my point. There is still backpressure, and it's still costing power. As long as we are talking about race cars and equivalent full race supercharged car would have 20psi at the inlet valve and 0psi (above ambient) just after the exhaust valve.
If anyone can prove me wrong about this, or anything on my site, I would love to hear from you. This is not some sort of arrogant challenge. I am truly interested to hear from you.
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